The invention relates to a glass encapsulation lid intended to be applied to a substrate supporting microelectronic or microelectrooptic components so as to form, with this substrate, a gas-tight package containing the said components.
The invention applies most particularly to an image-display and/or illumination panel comprising, on a substrate forming the rear face of the panel, at least one organic electroluminescent layer, electrodes for making an electrical current pass through this layer, and the encapsulation lid hermetically sealed onto the substrate so as to form a sealed package enclosing the said organic electroluminescent layer. Such a lid comprises a bottom, forming the front face of the panel, and rims, extending over the entire periphery, which form the sides of the panel and connect the front face to the rear face.
The organic light-emitting diode (OLED) layers are very sensitive to moisture. They therefore have to be encapsulated as soon as they have been manufactured, while these layers are in a controlled atmosphere protected from moisture and from oxygen. The encapsulation must be carried out at low temperature in order not to damage the organic layers that are deposited on a substrate. Usually, the OLED layers are encapsulated by bonding a lid to the substrate, using UV-curable adhesives. Another technique, less common, consists in applying, generally under vacuum, protective layers directly on the organic layers to be protected. It is also possible to use the two techniques simultaneously.
The lid used for the encapsulation may be made of metal or glass. For top-emitting OLEDs, the lid has to be transparent since the light emitted in the electroluminescent layer escapes from the panel on the opposite side to the substrate; such structures are particularly advantageous, especially because they allow high light extraction yields. For such structures, glass lids are therefore generally used.
Document U.S. Pat. No. 6,081,071 discloses an OLED panel provided with a glass substrate and encapsulated by a flat glass lid with no rims. The encapsulation requires the provision of an encapsulated space with a height generally between 0.4 mm and 1 mm between the substrate and the lid. The height of this space is needed for incorporating an adsorbent and/or desiccant agent in the encapsulation space. This adsorbent agent is designed to absorb the residual traces, especially of oxygen and water, in this space. Such an agent is sometimes also called a getter or a desiccating agent.
When a flat lid is used, an adhesive seal serves to establish the distance between the substrate and the lid, which is needed to provide this space, as is also disclosed in document U.S. Pat. No. 6,081,071. The reader may also refer to document US 2003/227253 and especially to FIGS. 5B, 6B and 7 of that document, which describe the use of sealing parts between the lid and the substrate, respectively referenced 512 and 609.
The substrate, the lid and the means for sealing the lid onto the substrate therefore form a gas-tight encapsulation package.
Owing to the very high sensitivity of organic OLED materials to moisture, it is desirable to minimize the thickness of this adhesive seal or the height of this sealing part, which provides the impermeable join between the substrate and the lid. This is because, since this seal or this part is made of an organic material (for example an epoxy resin), it will always be more permeable to moisture and/or oxygen than mineral materials, such as the glass forming the base of the substrate and of the bottom of the lid.
To minimize the thickness of the adhesive seal or the height of the sealing part, packages provided with rims are therefore used. The height of the rim replaces a portion of the height of the seal (see for example FIG. 7 of the abovementioned document U.S. 2003/227253). Such rims form, on the lid, a peripheral projection.
The manufacture of lids provided with rims is expensive. For example, they may be obtained by mechanical machining of a glass plate. This subtractive technique is all the more expensive and ill-suited the larger the size of the panel.
Moreover, it is known to make cavities or grooves in the internal face of the lid in order to be able to better house and distribute the adsorbent agent in the package. FIG. 6B of the abovementioned document U.S. 2003/227253 describes a cavity 608b in the lid 608a, while FIG. 4 of document U.S. 2004/056232 also describes a cavity 49 in the lid 43.
Document U.S. 2003/038590 and EP 1 411 562 also disclose, in the specific case of top-emitting panels, grooves that are made in the internal face of the transparent lid and placed between the pixels, in order to contain adsorbent agent. Documents U.S. Pat. No. 5,239,228 and JP 2002-050471 disclose top-emitting electroluminescent panels in which the transparent lid includes a single peripheral groove which is placed away from the active or emitting surface and which contains an adsorbent agent.
The manufacture of such grooves in glass plates is expensive. For example, they may be obtained by sandblasting, after the regions of the lid corresponding to the locations of the pixels have been masked.